1. Field of the Invention
The present invention relates to a shaft drive device and, more particularly to a technique which enhances an assembling property of a universal joint and a drive shaft to an output shaft of an engine. The present invention mainly relates to a shaft drive device which is favorably applicable to a motorcycle.
2. Description of Background Art
Conventionally, a shaft drive device is known that is capable of transmitting an output of an engine mounted on a vehicle body to a wheel by way of a drive shaft by connecting the drive shaft to an output shaft of the engine by way of a universal joint and by connecting the wheel to a distal end side of the drive shaft. See, for example, JP-UM-B-1-37353 and JP-A-2003-118675.
JP-UM-B-1-37353 (mainly FIG. 5) discloses a technique which, to facilitate a fitting engagement between a yoke joint (8) and a propeller shaft (6) at the time of reassembling, forms guide ribs (4d, 4e) which restrict the movement of the yoke joint (8) in the pull-out direction on an inner surface of a rear fork (4b) so as to maintain a spline fitting engagement between the yoke joint (8) and an output shaft (3a) of the engine when the propeller shaft (6) is pulled out from the rear fork (4b).
However, JP-UM-B-1-37353 does not disclose any technique which connects a yoke (8b) to an output shaft (3a) of an engine.
On the other hand, JP-A-2003-118675 (mainly FIG. 5 to FIG. 7) discloses a technique in which a universal joint (51) and a drive shaft (52) are connected with each other by fitting a male fitting portion (52a) formed on one end of the drive shaft (52) into a female fitting portion (74a) formed on an output-side yoke (74) extending from the universal joint (51). A length of the male fitting portion (52a) in the axial direction is set 1.5 to 3.0 times as large as a specific length L necessary for transmission of an output so as to produce a margin of movement of (0.5 to 2.0)×L. According to this technique, in connecting the universal joint (51) to the output shaft (48) of the engine, the universal joint (51) can be pulled out from a shaft storing portion (15) which houses the universal joint (51) and the drive shaft (52) therein and, while maintaining the connection of the universal joint (51) and the drive shaft (52), the universal joint (51) can be easily connected to the output shaft (48) of the engine.
The technique disclosed in the above-mentioned JP-A-2003-118675 cannot always easily connect the universal joint to the output shaft of the engine.
For example, when a working space provided for allowing an operator to grasp a yoke to be connected to an output shaft of an engine and to move the yoke to the output shaft side is narrow, both of a yoke grasping operation and a yoke moving operation become difficult. Thus, an operation for connecting the universal joint to the output shaft of the engine is not always easy.
Further, for example, when it is not desirable to slidably connect an output-side yoke of the universal joint and a drive shaft by spline fitting (for example, when a large output is to be transmitted), the technique disclosed in the above-mentioned JP-A-2003-118675 is not adoptable. Thus, the operation for connecting the universal joint to the output shaft of the engine becomes difficult.